Acetylcholine (ACh) has diverse regulatory roles in the central nervous system. Cholinergic neurons in brainstem and basal forebrain structures send ascending fibers throughout the brain where they may participate in a wide range of functions, including modulation of learning, memory retrieval, mood states, central autonomic control, and the processes regulating sleep/arousal. Mechanisms by which cholinergic signals induce long-lasting changes in neuronal state, and their consequences for behavior, are areas of intense research interest with great importance for human health. We propose to investigate mechanisms of cholinergic signaling via M1 mAChRs (M1.Rs) to behaviorally relevant hypothalamic neurons and immortalized cells from rat, as well as in transgenic mouse models. Imaging of M1.R distribution within the suprachiasmatic nucleus (SCN) reveals substantial receptor concentrations. We have found that M1 subtype-like pharmacological reagents selectively alter the cholinergic response. Preliminary data using transgenic mice and immortalized cell lines support the pharmacology and point to this brain site as an important model in which to evaluate M1.R signaling. We propose to employ techniques ranging from behavioral analyses to extracellular and patch-clamp recordings in brain slices, accompanied by immunocytochemical, biochemical and cell biological approaches, together aimed at uncovering fundamental mechanisms of M1.R signaling. Our specific aims include: 1) To fully evaluate the effect of genetic deletion of the M1.R on the cholinergic response, 2) To assess actions of downstream diffusible messengers, and 3) To define the role of specific PKG isoforms in this M1.R signaling cascade. In addition to making fundamental contributions to understanding muscarinic neuromodulation of CNS neurons, these studies will permit us to evaluate the roles of M1.R-mediated neurotransmission within a defined behavioral axis. This multidisciplinary approach will provide new insights into central cholinergic neurotransmission, muscarinic signal transduction mechanisms, and decision-making processes that form the neural substrates of behavioral change. Signal transduction is a cellular process, and by identifying the roles of specific receptors, second messenger systems and targets, we will be able to understand the causal mechanisms that mediate long-term adjustments in neuronal state. This research has applied relevance for strategies in developing rationally-based therapies for cholinergic disorders, including those altering sleep/arousal, autonomic function, senile dementia, Alzheimer's type (SDAT), Parkinson's disease, Huntingtons chorea and other neuropsychiatric and movement disorders.